A mechanical system in normal operational condition involves a certain number of motion-resisting forces arising from various phenomena. If the magnitudes of these forces can be established via measurement or calculation, then it is possible to utilize this information to optimize the operation of the system.
An elevator system comprises numerous mechanically movable parts that are subject to a number of forces resisting motion, such as e.g. frictional forces and the inertial and gravitational forces caused by movable masses. An elevator door that moves automatically on a horizontal rail is one of such parts, which is acted on by forces from different directions and is both at its upper and lower edges in contact with rails that keep the door motion on track. The magnitude of the forces resisting the motion of elevator doors varies between different elevator systems. Often the magnitude of these forces also changes during the operation of the elevator system. Direct continuous measurement of motion-resisting forces is often difficult to implement; for example, a separate “friction meter” can not be advantageously mounted on an elevator door. Therefore, the magnitude of each force resisting the door motion is preferably measured indirectly. It is possible to create a model of the system in question, i.e. in this case the elevator door, wherein the forces applied to the door are observed. The forces acting in the model include frictional forces resisting door motion, mass of the door and forces produced by the door closing device. By using the model, it is possible to calculate desired parameters when the magnitudes of the tractive forces opening and closing the door are known and the acceleration or velocity of the door is measured. This makes it possible to solve unknown parameters, such as frictional force, door mass and the horizontal force component applied to the door. When the above-mentioned parameters, the so-called kinetic parameters are known, door-operations such as opening and closing can be controlled accurately and in an optimal manner as regards the elevator system, thereby improving the performance of the elevator system. Thus, we are dealing with a problem of optimization and parameter estimation.
In an elevator system, the door assembly consists of a car door moving with the car and the landing doors on different floors. A modern automatic elevator door is opened and closed by a door operator integrated with the elevator car and using e.g. a direct-current motor to open and close the elevator doors at each floor level. The torque produced by the direct-current motor is directly proportional to the motor current. The energy of the motor is coupled to the door e.g. via a cogged belt, and the door slides on rollers. For reasons of safety, the landing door alone is closed without a motor by means of a closing device. The closing force of the closing device can be produced by a closing weight or a helical spring. The motor current and the corresponding torque are measured either from a motor controller card or directly from the motor current lead. Another motor parameter that can be monitored is the so-called tacho pulse signal. The tacho signal typically consists of a square wave whose frequency is dependent on the speed of the motor and therefore the door speed.
A problem with prior art is that the elevator system generally comprises a plurality of doors, whose kinetic parameters may vary widely between different doors. The number of parameters may also be large. For example, a building with 8 elevators serving 30 floors contains 240 doors, for each of which several kinetic parameters should be determined. In such cases, it is thus very laborious, often almost impossible to determine all the parameters. A prior-art solution is to define suitable kinetic parameters for the heaviest door in the elevator system when the system is commissioned and to use these parameters for the control of all doors in the elevator system. Typically, the heaviest door is located in the entrance lobby of the building and may weigh e.g. 130 kg, whereas the doors on the floor levels may have a mass of only 100 kg. In other words, in prior-art solutions no door-specific optimization of operations is performed. For example, the control parameters for the motor controller controlling door operation are not optimized, nor are the speed profiles of different doors in the elevator system. In the example case mentioned above, it is possible to increase the transportation capacity of the elevator system by 2.3% and to shorten the average passenger waiting time by 5% by optimizing the speed profile of the landing doors for a mass of 100 kg instead of 130 kg. A further drawback with prior-art solutions is that the door motor controller may oscillate as the motor load varies, causing unnecessary mechanical stress while the time needed to perform door operations increases unreasonably. Thus, there is a need for an automatic method for determining the kinetic parameters of the doors in an elevator system to optimize door operations so as to allow the performance of the elevator system to be improved.